Various processes for preparing tert-leucine, e.g. L-tert-leucine (Scheme 1, formula 1: R.sub.1 =R.sub.2 =R.sub.3 =Me) are known. See, for example, EP-A-0137372, EP-A-0248357, EP-A-0494716 and JP-A-63/211248.
Bevinakatti et al, J. Chem. Soc. Chem. Comm. (1990) 1091, and Tet. Asym. 3:1505 (1992), disclose enantioselective ring-opening of oxazolin-5-ones, and the effect of solvent on the ring-opening.
Sih et al, Tet. Lett. 33:1953 (1992), and J. Org. Chem. 58:3252 (1993), describe the enantioselective hydrolysis of oxazolin-5-ones and thiazolin-5-ones, in the context of asymmetric amino-acid synthesis.
U.S. Pat. No. 5,219,731 discloses a process for preparing optically-active amino acid derivatives comprising enantioselective enzymatic hydrolysis of oxazolone precursors, e.g. 5(4H)-oxazolone.